Some of the cases he investigated resulted in a decision not to file charges.
One of the most notable cases the public integrity section did pursue under his watch was the successful prosecution of the former Republican governor of Virginia, Bob McDonnell, on corruption charges — a conviction later overturned by the Supreme Court. He also oversaw the 2013 prosecution of a Republican congressman from Arizona, Rick Renzi, who was later pardoned by Mr. Trump.
Mr. Smith also helped direct the prosecution of Jeffrey Sterling, a former C.I.A. officer. He was convicted of mishandling national security secrets and of obstruction of justice in connection with accusations that he leaked information about a secret operation to sabotage Iran’s nuclear program to a reporter for The New York Times.
“Jack is not political at all,” said Lanny Breuer, the former assistant attorney general of the Justice Department’s criminal division, who recruited Mr. Smith to the job. “He is straight down the middle.”
Mr. Smith then worked as the No. 2 federal prosecutor in Nashville, before returning to Europe to work on war crimes cases.
For Mr. Trump, it will be a return to a familiar dynamic. The first half of his term, he faced a special counsel investigation led by Robert S. Mueller III, who scrutinized various links between his 2016 campaign and Russia.
Mr. Trump’s supporters have already accused the Justice Department under the Biden administration of investigating him for political reasons, and some Republicans have floated the idea of impeaching Mr. Garland if he pursues charges against the former president. That tension will only become more pronounced now that Mr. Trump is a candidate for president again.
The department has “a true conflict of interest, real or perceived,” said Claire Finkelstein, a law professor at the University of Pennsylvania and the founder of the Center for Ethics and the Rule of Law. “Garland won’t be running for president, but his direct boss will be. It would be difficult to put measures in place that would reassure people that the Justice Department was acting with independence on the Trump investigation.”
Katie Benner, Adam Goldman and Michael S. Schmidt contributed reporting.